I don't know what to do. I have a cat that I adopted from a shelter but she can not get along with the two cats I have. She attacks the other two and now they are scared to death of her. The new one is definitly the aggressor. My two hide behind the headboard of my daughters bed in a cubby and the new one goes back there and attacks them then leaves and sits out side it for a while waiting for them. Last week one of my cats spent three days under the couch. every time he showed his face he was chased back in. This has been going on for weeks now. They must be separated at all times. My two cats out during the day and the new one out at night. I called my vet and her suggestions were call a behaviorist ( which is not cheap ), use valium on the new cat for a while, or just give it up and take the cat back to the shelter. I dont't know what to do. Just the sound of the cat meowing sends my cats running.